Why are there no "easy" issues?

I brought my '89 Custom Cruiser (5-liter V8, RWD) into the shop to address the cold start stumbling I was having. They said that everything that can be adjusted was adjusted by them, but that the carburetor on the 307 is "sealed", leaving carb rebuilding as the only next step.

In my pile of meticulously-kept records (all the way back to its delivery inspection), the carburetor isn't mentioned as having had any problems at any time in her 168,000 + miles of life, so I certainly got my money's worth of work from that carb.

But before I spend the dough on a rebuilt unit (the only way they seem to come, no?) I want to run my symptoms down to see if we're barking up the right tree:

First start in the morning: Won't fire up without a few good pokes on the gas pedal and then won't STAY running without keeping the revs up. As this is happening it feels and sounds like it's down a few cylinders with its "rumpa rumpa rumpa" noise and engine wiggling/shaking.

But then, after just 15 or 20 secs., SOMETHING kicks in/opens up/whatever and the motor goes instantly smooth and it idles beautifully.

However, if you set off on your drive too "soon" you'll get a bogged-down feeling, with the engine nearly stalling (and the oil/choke light flickering) unless you put it in neutral and let her "warm up" some more.

Then everything is fine and you can drive all day without complaint.

EXCEPT: After leaving the freeway (if you've been on it for an extended period of time), when you slow to a stop at the end of the off ramp, that bogging-down feeling comes back with a vengeance and the "oil/choke" light lights up and stays on.

If you have to COMPLETELY stop you'll stall. But if you can keep her rolling, that stalling thing (and the warning light) will eventually go away (30 secs.?), leaving you right-as-rain again.

WTF is going on?!? Might a "new" carb solve this? What do they mean by "sealed"? Soon after purchasing her (3 months ago) she had a full workup--including testing oil pressure and replacing a leaky sending unit--and now everything is doing its job perfectly. So what's with the "oil/choke" light?

[They also said there might be a vacuum leak somewhere but there's no actual evidence of that. Oh, and she doesn't smoke, but her exhaust smells STRONGLY of unburnt fuel.]

I just know that one of you will have the answer to this, whatever it may be. I was raised on overhead cams and fuel injection and have no problem admitting that I'm out of my element here.

[MANY] thanks in advance as always,

Drew

 

Those carbs do have the mixture screws sealed and most mechanics do not want to drill out the seals or want to mess with it. Possible legal issues, but who cares about those!
20 years from a carb is good given the crappy corn-based gas we have now.
If it need rebuilding, I would pull it myself and send it to a reputable carb rebuilder if you do not want to do it yourelf. If the throttle bushings are worn, they can rebush them, too.
I do not like the generic rebuilt unit swap, but maybe it will work okay. Cost will be similar and the carb stays original to the car.
I would make sure they changed the TPS unit also when it is rebuilt - if not bad, it will be soon. Pain to change, too. No extra labor - maybe provide a new AC delco unit to them.

Make sure all the emission crap is hooked up and working - those tend to make the car do strange things. The EGR passage often gets blocked with carbon.

 

There are actually two adjustments that are sealed from the factory, the idle mixture screws and the idle bleed vent. The factory Chassis Service Manual describes the procedures for removing these seals and properly adjusting the carb. The process is pretty simple but requires removal of the carb. Frankly, I doubt there are many shops that even know how to properly adjust the CCC system. Even a rebuilt carb will require these adjustments.

If you don't already have a factory CSM, get one. Then find a shop that will read, understand, and follow the adjustment process described in the manual. I've done this on my two CCC 307s and while the process is not difficult, it does require attention to detail and following the procedure exactly as described in the manual. It also requires that every single part of the CCC system, including the miles of vacuum hose, be in operating condition. There are several dozen possible failure modes in the system that can cause poor running, none of which show up as computer error codes. It is a rare repair shop today that knows how to properly diagnose a problem that isn't spoon-fed from the computer.

 

I'll just throw this in. I am not familiar with an 89 307 engine, but I had a chevy 350 (with standard steel timing chain) that was having nearly identical symptoms as you describe. I put on a new carb to no avail, it still had all the problems. Turns out the timing chain had stretched so far and was so loose that when cold, the engine would run like crap, etc. etc. just as you describe, and if you dared to try and put any load on the engine (putting in drive or reverse before the 10 min warmup) it would run even worse or quit all together. Amazingly once warmed up it would run pretty well, unless you floored it. Then the process would start again, engine would die, and as long as you waited a while for the carb to clear, it would start right up.
Long story longer, the cold, loose timing chain would jerk the cam timing around just enough to throw everything off, and it seems, sounds, feels, for all the world like a carb problem. Once the chain warmed it would settle into a somewhat "normal" (without all the slap) ryhthm and the motor would run pretty well.
I put on a new timing chain and gears and re set the timing and the motor ran like a top. For what it's worth.

 

The above can possibly happen with the Olds engines, too. I think the timing chain should be replaced at least every 100k miles.

 

That's a good point. I usually only go 80,000 miles on a stock timing set with plastic cam gear. The CCC 307 does have a number of carb and CCC system have a number of failure modes that are unique to that motor, the basic mechanical condition of a high mileage motor should always be checked.

 

Mine's more the "rurr rurr rurr" that lasts longer in direct proportion to the number of days she's been sitting, as in if you drove her the day before she starts after a handful of "rurrs" while after four days it'll seem to take FOREVER (which help prove that you have a good battery and starter...).

[You have to pump the gas pedal like mad the whole time, too, thus my carb-replacement focus of late.]


Add in the fact that once she gets hot (or basically after more than 10 mins. of running), the jerking, stumbling and stalling you mentioned starts in. Putting her in neutral keeps her alive, and after a few minutes of even parking lot cool down she's back to smooth running.

It corresponds to her "OIL/CHOKE" dash light at first flickering, then solid on, "BONG BONG" and all. Her oil level hot and cold is fine, so obviously it's a cluster***k under the hood. Still, I'd like to get a handle on it before the snow falls.

Ideas? Know anyone that knows Olds' within 100 miles of Detroit? Anyone?...

 

Pumping the gas is a sign of choke trouble, if excess pumping is required to start.

 

I am 65 miles from Detroit...